1. Field of the Invention
The invention relates to a radiological installation having means for compressing the dynamics of the radiological image for making better use of the dynamics proper to the image acquisition means, such more especially as a television camera.
2. Description of the Prior Art
In medical radiology, in particular in the field of vascular radiology, it is often desirable to be able to compress the overall contrast of the radiological image so as to be able to reveal certain details. In fact, such dynamic compression then allows the grey scale of the image acquisition means to be fully used. For that, acting on the path of the X rays is known by disposing, between the X ray source and the patient, X ray absorbing elements whose characteristics compensate at least partially for the differences of attenuation in the object. An image resulting from this treatment is then acquired by the display chain and known image subtraction processing may then be applied under good conditions. More precisely, a reference image is taken and stored, for example before injection of a contrast product. It is then subtracted systematically from the following ones so that the circulatory arborescence invaded by the contrast product appears with very great clearness. All of this processing gives good results but requires considerable and expensive electronic means with risks of prolonged exposure to the X rays not only for the patient but also for the person who handles the absorbing elements, during the period of adjustment thereof.
There is also known the technique of "unsharp mask" perfected for radiographic films. This method consists in making a reverse print of the film and superimposing the two prints for the final proof thus achieving a certain dynamic compression. The invention proposes more particularly transposing this concept, using means of a different kind, in a radiological installation comprising means for optical transmission between an output screen of a radiological image receiver (for example a luminance amplifier) and image acquisition means (for example a television camera). The basic idea of the invention consists then in carrying out the dynamic compensation processing in the optical path of the image (by generating therein a sort of unsharp mask), upstream of the acquisition means whose proper dynamics would be too limited for precise acquisition of low contrasts.